Saint Joan is one of those plays that, if you've read it before seeing it, you can't ever imagine in performance. It's so wordy, so indigestibly stuffed with ideas, and the characters are so thoroughly described in stage directions, rather than through their lines, that it seems inextricably tied to the page. It's an achievement just to keep it alive on stage for the whole three hours; but Gale Edwards' Theatr Clwyd production, now moved to the Strand, does considerably better than that, exposing behind all Shaw's verbiage and lecturing the play's sheer dramatic sweep.

Much of the sense of epic derives from Peter J Davison's design, which encloses the main acting area in massive, plain blocks of stone. These lift one at a time to create doors or reveal a series of beautifully composed tableaux (Joan, sword aloft, silhouetted against a huge cross of light; a red pennant floating against a mauve-tinged sky before Orleans). There are objections to be made to the detail of the design - what's the point of the slogans running around the walls, or the shining, empty breastplates ranked across the stage at the beginning? - but as a canvas for the actors to work with it functions brilliantly.

The only real disappointment is Imogen Stubbs's Joan. With her north-eastern accent, her unshakeable self- belief and her constant exhortations to get out and fight, she is oddly reminiscent of Jack Charlton (the main difference being that he has had a better relationship with the papacy). As far as it goes, that's surely pretty close to what Shaw wanted - somebody down-to-earth and practically minded. But it doesn't go far enough. She's too light to suggest the Maid's real strength: where she should seem fanatical and charismatic, she comes across as earnest and charming.

And while Stubbs gets plenty of individual moments well - her collapse before the threat of burning, say - she doesn't manage to give a sense of the role's arc, so to speak. Instead of character development, you get a series of ever- grimmer haircuts, shifting from long and flowing at the start, through short back and sides for her glory days, to a ragged crop for prison.

It's a measure of the strength of the production, though, that reservations about Stubbs's performance don't spoil your enjoyment of the play. The only other major part that leaves qualms is Jasper Britton's slouching, narrow Dauphin - he's very funny, but the tendency to caricature dilutes the impact of his appalling self-knowledge (he accepts her imposition of kingship with the qualification 'I shan't be able to keep it up, I warn you').

Otherwise, the supporting cast is uniformly fine, particularly Ken Bones as the Earl of Warwick - relaxed and predatory, indicating a powerful, pragmatic intellect holding in check a natural ferocity.

The most impressive thing, though, is how well Shaw's play has survived 70 years. True, it's at times hectoring and prolix, the political analysis unconvincingly reductive. But his jibes against the English still hold water (as when Warwick softens the word 'traitor' with the explanation: 'In our country it means simply one who is not wholly devoted to our English interests'); and in the way the self-interest of the ruling class is dressed up as realism, you may hear an unpleasantly contemporary ring.